This invention relates to a roller-tip, rocker-arm for internal combustion engines, and, more particularly, to such a rocker-arm having a special perpendicular geometry at valve mid-lift to improve engine performance.
In internal combustion engines it is conventional to provide valves, for the fuel-intake and combustion gas-outlet ports of the engines' combustion cylinders, which are spring-biased to seat and close the respective ports and have upwardly extending stems that, through pivotally mounted rocker-arms contacting and abutting the respective ends of each, are caused to be depressed by the controlled upward movement of cam-driven pushrods, the rocker-arms being provided with trunnions, about which the rocker-arms pivot, mounted on the engine by stud elements that extend upwardly through the rocker-arm and trunnion combinations. By means of such an arrangement, the position or amount of "lift" being imparted to a given valve, at a particular time in the operation of the engine, by its respective pushrod and rocker-arm depends upon the shape of the cam lobe, on the cam shaft operating the valve system, allocated for that valve. Since the end of the rocker-arm contacting the valve stem (i.e., the "nose" of the arm) and the end thereof contacting the pushrod (i.e., the "tail" of the arm) each is a fixed distance from the trunion axis about which the arm pivots during its movement, in the operation of such a valve system there necessarily is some under-arcing and/or over-arcing of the arm nose and tail during engine operation, resulting in frictional contact between the abutting surfaces, particularly at the arm nose and spring-biased stem contact, that unsatisfactorily contributes to component wear and even failure, but, at a minimum, to loss of engine performance. Such problems become more aggravated in high performance, high r.p.m. engines, such as those employed in drag racing. Trans-Am competition, boat racing, and other motorsports competition, due to the attendant increased reciprocation of the rocker-arm and also due to the use of stronger springs and sharper valve cam lobe shape changes demanded by such engines.
In an attempt to minimize such difficulties, various approaches have been suggested previously, including the location of a roller at the nose of the rocker-arm, exemplified by that shown in U.S. Pat. No. 3,466,073, and the use of particular alloys in the components, which are more expensive.
Such prior attempts, however, have not proven to be completely successful, since, due to apparent mis-assumptions regarding arm design consequences and an apparent desire to try to adapt "stock" rocker-arms to variously sized engines, little or nothing has been done to remedy the over-arcing problem, with the result that conventional rocker-arms remain to be characterized by motion of the arm nose and/or pushrod which exceeds the ideal (i.e., minimum) by levels ranging up to and over 30% and even as high as several hundred percent. Furthermore, the substitution of certain "stronger" alloys has also introduced more flexibility into the arm; so, such prior proposals have continued to be plagued by component wear and fracture problems and additional engine performance limitations such as premature valve float. Similarly, since such previous suggestions have failed to provide a suitable solution to the difficulties now traceable to the over-arcing characteristic, no discernible effort has been made heretofore to decrease the length of the pushrod side of the arm relative to the length of the valve side, under optimum arcing conditions, and others have been forced to retain the utilization of pushrod cams having relatively sharp lobe shapes which contribute to significantly high lifter motion, pushrod motion, and lifter violence and limited valve acceleration.
Accordingly, a search has continued in the art for an improved rocker-arm which can allow improved engine performance.